FluxBat is an ACPI based battery monitor for the fluxbox window manager. It includes two parts: a daemon process that runs the update script and the update script itself. The whole software contains only about 100 lines of code and is easy to use by including only one line in the menu configuration file of fluxbox.
PowerTop is tool that detects which Linux programs and kernel tunables are resulting in the largest power consumption and use of battery time. By fixing (or closing) these applications or processes, you can immediately see the power savings in the tool. You'll also see the estimated time left for battery power if you are running a laptop.
ZUPS allows for monitoring the state of one or more UPS devices using SNMP and executing user-specified commands in case of power outage, such as email notifications and controlled remote host shutdowns. If the UPS devices are running on battery, the shutdown commands are executed for an arbitrary number of remote hosts, optionally with some delay specified for each host. ZUPS can be configured to ignore these delays and run the specified commands immediately if the UPS devices are running out of battery power. Custom plugins can easily be added in order to perform other checks.
asapm is an AfterStep look & feel Advanced Power Management (APM) monitor for laptop and notebook PCs running Linux or FreeBSD/NetBSD/OpenBSD and X Windows. It displays charge left in the battery, the time left to the total discharge of the battery, computer is connected to the mains or is working on a battery and the battery status high/low/critical.
MonAMI aims to be a standard place for monitoring the availability and performance of services. It can talk to many different monitoring systems while remaining easy to configure. It has a plugin structure, making it easy to add new things to monitor or to integrate with new monitoring systems.
Suspend2 allows you to hibernate your machine without needing APM, BIOS, or ACPI support. It creates an image that is saved in your active swap partitions, swap files, ordinary files or (soon) across a network. At the next system boot, the kernel detects the saved image, restores the memory from it and then it continues to run as if you'd never powered down.